1. Field of the Invention
The invention pertains to the field of conveyor technology, in particular to the conveyance of planar products like, e.g., print shop products.
2. Description of Related Art
In the production of planar products, in particular print shop products, as a rule it is necessary to transfer the products from one conveyor device to another. For overcoming great distances of conveyance, or for separation for the purposes of handling, the further conveyor device is often a gripper conveyor in which many grippers are moved along a closed orbital track. One such device, with which it is possible to transfer products that are delivered by a feeder device in the form of a belt conveyor to a gripper conveyor, is for example disclosed in EP-A 0557 680 or CH 655 488. The arriving products, which are in an imbricated formation, are individually gripped by each respective gripper in a transfer area of a curved or straight orbital track. For this purpose, the parts of each gripper are movable from an open position to a closed position, and vice-versa. Control is provided by a stationary control guide (opening-closing guide) that interacts with a control element on the gripper, e.g. a control cam or a slide. Depending on the design of the grippers, their orientation with respect to the orbital track can also be adjusted by means of a control guide. The position along the orbital track at which the grippers are closed or opened, and if applicable the change in orientation that is attained by the gripper, is determined by the shape and location of the corresponding control guide. In known conveyor systems, the control guide is stationary, such that all the grippers go through the same movement and thus at the same opening- and/or closing location open and/or close, and/or are pivoted in a similar manner.
In the processing of planar products, in particular print shop products, it can occur that defective products are found in the conveyor stream. These should be rejected from the conveyor stream at the earliest possible point in time, so as not to disrupt further production and conveyance activities. This problem arises, for example, when print shop products are wrapped in a common wrapping film: if the casing or number of products is faulty, the packet of individual products can fall apart when transported further by means of a gripper conveyor. If possible, such a packet should therefore be ejected from the conveyor stream subsequent to the erroneous preceding step and before the transfer of the product to the gripper conveyor. With the conveyor systems that are known until now this is only possible to achieve by moving the feeder device as a whole into a position in which the grippers can not take up the product, e.g. by rotating it out of the transfer area in the manner of a see-saw. This is mechanically complex.